1. Field of the Invention
The invention relates to a device for displacing the movable parts of rail switches or crossings, in which a plurality of hydraulic cylinder piston units engaging in an offset manner in the longitudinal direction of the rails are each connected in series, wherein at least one directional or seat valve capable of being adjusted in a pressure controlled manner is inserted in the duct that connects the hydraulic cylinder piston units arranged in series.
2. Prior Art
A device of the initially defined kind may already be taken, for instance, from WO 96/34786. In that known device for setting switches, a plurality of cylinder piston units are provided, which may be connected in parallel or in series. In the event that such cylinder piston units are connected in series, push-open valves are described in WO 96/34786, which ensure that, after a hydraulic cylinder piston unit has been shifted completely, the hydraulic pressure required for displacement is transmitted directly into the respective working volumes of consecutive hydraulic cylinder piston units. During shifting, the actuation of consecutively arranged hydraulic cylinder piston units usually is effected by means of the pressure of the fluid volume displaced out of a preceding hydraulic cylinder piston unit.
During the displacement of movable parts of rail switches or crossings, the pressure applied at first is effective in one of the working volumes of the respective actuating cylinder, multiplicaton of that pressure by the respectively active piston surface resulting in the actuating force. Said actuating force is counteracted by displacement resistances, such resistances being likely to cause a rapid increase in pressure, in particular at a blockage of the displacement movement. In order to secure the overall hydraulic system, it is therefore known to centrally provide pressure control valves, such a configuration being described, for instance, in DE 21 44 564 A1. Inadmissible operating conditions, however, will only insufficiently be detected by means of such a pressure control valve, since pressure control valves of that type have to be designed for a working pressure that is higher than the sum of the displacement resistances or resistance forces of the hydraulic cylinder piston units connected in series.
In the device that has become known from EP 778 191 A2, safety means are provided, which, as the displacement movement is being interrupted, render the individual cylinder piston units pressureless to such an extent that thermal expansions may be taken into account. Such a configuration does not provide any automatic cutoff in the event that inadmissible operating conditions of individual cylinder piston units are exceeded.
The invention aims to further develop a device of the initially defined kind, comprising hydraulic cylinder piston units connected in series, to the extent that any inadmissible operating conditions will be recognized early and in time and any further displacement of the switch actuator will be stopped if the admissible resistance force acting on a hydraulic cylinder piston unit is exceeded. To solve this object, the configuration according to the invention essentially is characterized in that, if a preset difference of the pressures prevailing in oppositely arranged working volumes of the same, preceding cylinder piston unit is exceeded, the directional or seat valve blocks the connection to the consecutive cylinder piston unit. Due to the fact that the directional or seat valve capable of being adjusted in a pressure controlled manner, which is inserted in the duct that interconnects the hydraulic cylinder piston units arranged in series, blocks if a preset difference of the pressures prevailing in oppositely arranged working volumes of the same, preceding cylinder piston unit is exceeded, any inadmissible rise in the differential pressure as occurs on account of an elevated displacement resistance will be recognized in time and, due to the fact that in those cases the connection to the consecutive cylinder piston unit is blocked immediately, any further displacement movement of switch will be reliably stopped such that inadmissible deformations can be excluded.
Advantageously, the configuration is devised such that a directional or seat valve capable of being adjusted in a pressure controlled manner is each inserted in the supply duct and in the discharge duct of at least one hydraulic cylinder piston unit, the displacement actuator of which directional or seat valve is powered by the pressure prevailing in different working volumes of the same cylinder piston unit, wherein, in particular, the circuitry in a particularly advantageous manner is realized such that the valves of the individual cylinder piston units are each controlled in a manner that the valve opening into a working volume is powered by the pressure prevailing in the oppositely arranged working volume of the same cylinder piston unit. In order to displace a movable part of a rail switch or crossing, a working pressure p1 aimed to shift the piston in the sense of the displacement movement enters into effect in one hydraulic cylinder piston unit each. Said working pressure p1 which, multiplied by the respectively active cross sectional area A of the piston, defines the actuating force F is counteracted by the force of the shift resistance FW. From the working volume arranged opposite the working volume that is powered by the pressure p1, fluid under a pressure p2 that corresponds to the reduction caused by the force corresponding to the external resistance is pressed out into the working volume of a consecutive cylinder piston unit for a displacement movement in the same direction, that pressure difference not constituting any problem as long as the displacement resistance occurring remains within defined limits. In detail, the following relations apply:
p1xc2x7A=p2xc2x7A+FW
(p1xe2x88x92p2) A=FW
xcex94pxc2x7A=FW
wherein, in the above equations, p1 represents the working pressure prevailing in the respective cylinder piston unit concerned and p2 refers to the pressure of the fluid displaced out of the oppositely arranged working volume of the same cylinder piston unit. The pressure difference occurring is proportional to the shift resistance, wherein, due to the fact that this pressure difference is then used for controlling the respective valve, transmission to the consecutive hydraulic cylinder piston unit will be blocked if this pressure difference exceeds a predetermined value. The directional or seat valves powered by the respective pressure difference in that case may be united to a structural unit directly with one hydraulic cylinder piston unit each and are able to respond to inadmissible operating conditions as may occur in connection with an individual one of a plurality of hydraulic cylinder piston units connected in series.
The respectively last one of a plurality of hydraulic cylinder piston units arranged in series may be so designed as to not include any additional valves, wherein the configuration in a particularly simple manner is devised such that the hydraulic cylinder piston unit arranged last in the series connection is connected directly with the valves of preceding cylinder piston units.
In the main, the configuration according to the invention always causes the downstream valve to be closed as the pressure difference occurring has reached the admissible extent defined by the resistances under normal operation. In order to minimize the specific resistances in a plurality of such hydraulic cylinder piston units connected in series, it is advantageous to reduce the lengths of the respective return ducts. To this end, the configuration advantageously is devised such that the series connection in the event of more than three hydraulic cylinder piston units connected in series is realized in a manner that the working volume of a hydraulic cylinder piston unit is connected with the working volume of a hydraulic cylinder piston unit after next, with the valves being arranged therebetween. In this manner, the lengths of the return ducts can each be minimized so as to ensure precise responding.